[move-function] Update async dbginfo for upstream LLVM change.
[move-function] Update async dbginfo for upstream LLVM change.

I changed code upstream so that we are always guaranteed to have an entry value
for async arguments on r14. The main effect of this is that it eliminates a bunch of
cases where r14 would be spilled simplifying weird patterns in the test cases.

I also added additional commentary to the Dwarf part of the test cases
explaining what the patterns are checking and why.

roambotics/swift,atrick/swift,glessard/swift,gregomni/swift,roambotics/swift,ahoppen/swift,benlangmuir/swift,JGiola/swift,atrick/swift,benlangmuir/swift,gregomni/swift,atrick/swift,glessard/swift,ahoppen/swift,glessard/swift,apple/swift,roambotics/swift,apple/swift,glessard/swift,apple/swift,roambotics/swift,benlangmuir/swift,gregomni/swift,benlangmuir/swift,atrick/swift,ahoppen/swift,gregomni/swift,benlangmuir/swift,atrick/swift,roambotics/swift,glessard/swift,apple/swift,JGiola/swift,ahoppen/swift,JGiola/swift,apple/swift,JGiola/swift,benlangmuir/swift,JGiola/swift,gregomni/swift,JGiola/swift,gregomni/swift,glessard/swift,roambotics/swift,atrick/swift,ahoppen/swift,apple/swift,ahoppen/swift